The present invention relates to a method for controlling data writing in a magnetic recording subsystem which uses a data buffer unit, and more particularly to method and apparatus for controlling data writing suitable for preventing an error in writing data into a magnetic recording media in a magnetic recording apparatus.
A magnetic tape and a magnetic disk have been known as magnetic recording media. The magnetic tape is referred to in the present invention.
FIGS. 3A and 3B show examples of prior art cartridge type magnetic tape subsystems. In the cartridge type magnetic tape subsystem of FIG. 3A, data transfer between a channel unit 2 and a channel interface control 3, and write/read operations between a write circuit 5 and a read circuit 6, and a magnetic tape unit 11 are effected time-serially. A long start/stop time for the magnetic tape is required in the write/read operations. The write/read operations require a longer time than the data transfer, and a data processing speed of the magnetic tape subsystem is limited by the write/read speed. In the cartridge type magnetic tape subsystem of FIG. 3B, a data buffer 4 is provided between the channel interface control 3, and the write circuit 5 and the read circuit 6. In the subsystem of FIG. 3B, when transferred data is to be written, a plurality of blocks are stored in the data buffer in the magnetic tape control unit and those blocks are collectively written into the cartridge type magnetic tape unit.
In the cartridge type magnetic tape subsystem of FIG. 3B, the number of times of start/stop operations of the magnetic tape unit is reduced to avoid reduction of operation efficiency of the system due to frequent repetition of the start/stop operations in order to efficiently operate the system.
JP-A-57-161956 discloses an invention which relates to the above prior art.
In the prior art, no attention has been paid to check whether the plurality of write data blocks temporarily stored in the data buffer in the magnetic tape control unit have been surely written into a designated one of a plurality of magnetic tape units. As a result, there may be an error in which the data are written into a different magnetic tape unit than the designated one or data at a wrong location on the data buffer are written. In the magnetic tape subsystem of FIG. 3B, the data buffer is provided in order to improve the data processing speed of the overall magnetic recording subsystem. As a result, the necessity to check the error in writing data has increased.
As the computers have been commonly used, the magnetic recording subsystems are used in bank transaction computation, payroll computation and parts ordering in a manufacturing process. In those areas, a severe reliability is required to the magnetic recording subsystems.
The present invention intends to resolve the problems encountered in the prior art and it provides method and apparatus for controlling data writing in a magnetic recording subsystem which assure exact writing of data blocks stored in a data buffer of a magnetic recording unit into a designated magnetic recording unit (for example, magnetic tape unit, or magnetic disk unit).